Metal gate structure of a CMOS semiconductor device and method of forming the same

ABSTRACT

A semiconductor device includes a substrate with an isolation region surrounding a P-active region and an N-active region, a first gate electrode comprising a first metal composition over the N-active region, and a second gate electrode with a center portion over the P-active region and an endcap portion over the isolation region. The endcap portion includes a first metal composition, and the center portion includes a second metal composition different from the first metal composition, and the center portion and the endcap portion do not overlap. An inner sidewall of the endcap portion is substantially aligned with a sidewall of the isolation region.

PRIORITY CLAIM

This application is a continuation of U.S. application Ser. No.15/356,736, filed Nov. 21, 2016, now U.S. Pat. No. 10,840,149, issuedNov. 17, 2020, which is a continuation of U.S. application Ser. No.14/733,038, filed Jun. 8, 2015, now U.S. Pat. No. 9,508,721, issued Nov.29, 2016, which is a divisional of U.S. application Ser. No. 13/189,232,filed Jul. 22, 2011, now U.S. Pat. No. 9,070,784, issued Jun. 30, 2015,which are incorporated herein by reference in their entireties.

FIELD

The disclosure relates to integrated circuit fabrication and, moreparticularly, to a metal gate structure.

BACKGROUND

As the technology nodes shrink, in some integrated circuit (IC) designs,polysilicon gate electrodes are replaced by metal gate electrodes toimprove device performance with the decreased feature sizes. One processof forming a metal gate structure is termed a “gate last” process inwhich the final gate structure is fabricated “last” which allows forreduced number of subsequent processes, including high temperatureprocessing, that must be performed after formation of the gate.

However, there are challenges to implement such features and processesin complementary metal-oxide-semiconductor (CMOS) fabrication. As thegate length and spacing between devices decrease, these problems areexacerbated. For example, in a “gate last” fabrication process, it isdifficult to achieve a perfect isolation between neighboring transistorsbecause unwanted recesses are generated in an inter-layer dielectric(ILD) layer after wet/dry etching a dummy strip. The recesses present inthe ILD layer can become a receptacle of metals during subsequentprocessing thereby increasing the likelihood of electrical shortingand/or device failure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features in the drawingsmay be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a flowchart of a method of fabricating a CMOS semiconductordevice comprising a metal gate structure according to various aspects ofthe present disclosure;

FIG. 2 is a top view of a CMOS semiconductor device comprising a metalgate structure according to various aspects of the present disclosure;

FIGS. 3A-3F are cross-section views of a CMOS semiconductor device takenalong the line a-a of FIG. 2 at various stages of fabrication accordingto various aspects of the present disclosure; and

FIG. 4 is a top view of a CMOS semiconductor device comprising a metalgate structure according to various aspects of the present disclosure.

DETAILED DESCRIPTION

It is understood that the following disclosure provides many differentembodiments, or examples, for implementing different features of thedisclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Forexample, the formation of a first feature over or on a second feature inthe description that follows may include embodiments in which the firstand second features are formed in direct contact, and may also includeembodiments in which additional features may be formed between the firstand second features, such that the first and second features may not bein direct contact. Various features may be arbitrarily drawn indifferent scales for simplicity and clarity. Further, the presentdisclosure may repeat reference numerals and/or letters in the variousexamples. This repetition is for the purpose of simplicity and clarityand does not in itself dictate a relationship between the variousembodiments and/or configurations discussed. In addition, the presentdisclosure provides examples of a “gate last” metal gate process,however, one skilled in the art may recognize applicability to otherprocesses and/or use of other materials.

FIG. 1 is a flowchart of a method 100 of fabricating a complementarymetal-oxide-semiconductor (CMOS) semiconductor device 200 comprising ametal gate structure 210 (shown in FIG. 2) according to various aspectsof the present disclosure. FIG. 2 is a top view of a CMOS semiconductordevice 200 comprising a metal gate structure 210 according to variousaspects of the present disclosure; and FIGS. 3A-3F are cross-sectionviews of a CMOS semiconductor device 200 taken along the line a-a ofFIG. 2 at various stages of fabrication according to various aspects ofthe present disclosure. It is noted that part of the CMOS semiconductordevice 200 may be fabricated with CMOS technology processing.Accordingly, it is understood that additional processes may be providedbefore, during, and/or after the method 100 of FIG. 1, and that someother processes may only be briefly described herein. Also, FIGS. 1through 3F are simplified for a better understanding of the presentdisclosure. For example, although the figures illustrate a metal gatestructure 210 for the CMOS semiconductor device 200, it is understoodthe CMOS semiconductor device 200 may be part of an integrated circuit(IC) that may comprise a number of other devices comprising resistors,capacitors, inductors, fuses, etc.

FIG. 2 is a top view of a CMOS semiconductor device 200 comprising ametal gate structure 210 fabricated by a “gate last” process. Asubstrate 202 (shown in FIG. 3A) comprising an isolation region 206surrounding a P-active region 204 p and an N-active region 204 n isprovided. The CMOS semiconductor device 200 comprises a p-type metaloxide semiconductor field effect transistor (pMOSFET) 200 p and ann-type metal oxide semiconductor field effect transistor (nMOSFET) 200n.

The nMOSFET 200 n is formed from an N-metal gate electrode 210 ncomprising a first metal composition 210 f over the N-active region 204n. In one embodiment, the first metal composition 210 f may comprise anN-work-function metal. In some embodiment, the N-work-function metalcomprises Ti, Ag, Al, TiAl, TiAlN, TaC, TaCN, TaSiN, Mn, or Zr. In thepresent embodiment, the N-metal gate electrode 210 n over the N-activeregion 204 n has a second width W₂ in the range of about 10 to 30 nm andextends outside of the N-active region 204 n over the isolation regions206.

The pMOSFET 200 p is formed from a P-metal gate electrode 210 pcomprising a bulk portion 210 b over the P-active region 204 p and anendcap portion 210 e over the isolation region 206, wherein the endcapportion 210 e comprises the first metal composition 210 f and the bulkportion 210 b comprises a second metal composition 210 s different fromthe first metal composition 210 f. In at least one embodiment, thesecond metal composition 210 s may comprise a P-work-function metal. Insome embodiment, the P-work-function metal comprises TiN, WN, TaN, orRu. In the present embodiment, the P-metal gate electrode 210 p over theP-active region 204 p has a first width W₁ in the range of about 500 to1000 nm, so that the first width W₁ of the P-metal gate electrode 210 pis greater than the second width W₂ of the N-metal gate electrode 210 n.In at least one embodiment, a ratio of the first width W₁ to the secondwidth W₂ is from about 18 to 30. The P-metal gate electrode 210 p andN-metal gate electrode 210 n are combined and hereinafter referred to asa metal gate structure 210.

Referring to FIGS. 1 and 3A, the method 100 begins at step 102 wherein asubstrate 202 comprising the isolation region 206 surrounding theP-active region 204 p and N-active region 204 n is provided. Thesubstrate 202 may comprise a silicon substrate. The substrate 202 mayalternatively comprise silicon germanium, gallium arsenic, or othersuitable semiconductor materials. The substrate 202 may further compriseother features such as various doped regions, a buried layer, and/or anepitaxy layer. Furthermore, the substrate 202 may be a semiconductor oninsulator such as silicon on insulator (SOI). In other embodiments, thesemiconductor substrate 202 may comprise a doped epi layer, a gradientsemiconductor layer, and/or may further include a semiconductor layeroverlying another semiconductor layer of a different type such as asilicon layer on a silicon germanium layer. In other examples, acompound semiconductor substrate may comprise a multilayer siliconstructure or a silicon substrate may include a multilayer compoundsemiconductor structure.

In the present embodiments, the semiconductor substrate 202 may comprisethe isolation region 206 surrounding the P-active region 204 p for thepMOSFET 200 p and N-active region 204 n for the nMOSFET 200 n. Theactive regions 204 p, 204 n may include various doping configurationsdepending on design requirements. For example, the P-active region 204 pis doped with n-type dopants, such as phosphorus or arsenic; theN-active region 204 n is doped with p-type dopants, such as boron orBF₂.

Isolation regions 206 may be formed on the substrate 202 to isolate thevarious active regions 204 p, 204 n from each other. The isolationregions 206 may utilize isolation technology, such as local oxidation ofsilicon (LOCOS) or shallow trench isolation (STI), to define andelectrically isolate the various active regions 204 p, 204 n. In thepresent embodiment, the isolation region 206 comprises a STI. Theisolation regions 206 may comprise materials such as silicon oxide,silicon nitride, silicon oxynitride, fluoride-doped silicate glass(FSG), a low dielectric constant (low-k) dielectric material, and/orcombinations thereof. The isolation regions 206, and in the presentembodiment, the STI, may be formed by any suitable process. As oneexample, the formation of the STI may include patterning thesemiconductor substrate 202 by a photolithography process, etching atrench in the substrate 202 (for example, by using a dry etching, wetetching, and/or plasma etching process), and filling the trench (forexample, by using a chemical vapor deposition process) with a dielectricmaterial. In some embodiments, the filled trench may have a multi-layerstructure such as a thermal oxide liner layer filled with siliconnitride or silicon oxide.

Still referring to FIG. 3A, a gate dielectric layer 208 may be formedover the substrate 202. In some embodiments, the gate dielectric layer208 may comprise silicon oxide, silicon nitride, silicon oxy-nitride, orhigh dielectric constant (high-k) dielectric. High-k dielectricscomprise certain metal oxides. Examples of metal oxides used for high-kdielectrics include oxides of Li, Be, Mg, Ca, Sr, Sc, Y, Zr, Hf, Al, La,Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or mixtures thereof.In the present embodiment, the gate dielectric layer 208 is a high-kdielectric layer comprising HfO_(x) with a thickness in the range ofabout 10 to 30 angstroms. The gate dielectric layer 208 may be formedusing a suitable process such as atomic layer deposition (ALD), chemicalvapor deposition (CVD), physical vapor deposition (PVD), thermaloxidation, ultraviolet (UV)-ozone oxidation, or combinations thereof.The gate dielectric layer 208 may further comprise an interfacial layer(not shown) to reduce damage between the gate dielectric layer 208 andthe substrate 202. The interfacial layer may comprise silicon oxide.

In a gate last process, a dummy gate electrode layer 308 is subsequentlyformed over the gate dielectric layer 208. In some embodiments, thedummy gate electrode layer 308 may comprise a single layer or multilayerstructure. In the present embodiment, the dummy gate electrode layer 308may comprise poly-silicon. Further, the dummy gate electrode layer 308may be doped poly-silicon with the uniform or gradient doping. The dummygate electrode layer 308 may have a thickness in the range of about 30nm to about 60 nm. The dummy electrode layer 308 may be formed using alow-pressure chemical vapor deposition (LPCVD) process. In at least oneembodiment, the LPCVD process can be carried out in a standard LPCVDfurnace at a temperature of about 580° C. to 650° C., and at a pressureof about 200 mTorr to 1 Torr, using silane (SiH₄) or dichlorosilane(SiH₂Cl₂) as the silicon source gas.

The method 100 in FIG. 1 continues with step 104 in which the structurein FIG. 3B is produced by forming a first dummy strip 308 a over theP-active region 204 p and isolation region 206 and a second dummy strip308 b over the N-active region 204 n in an inter-layer dielectric (ILD)layer 306.

In the present embodiment, a layer of photoresist (not shown) is formedover the dummy gate electrode layer 308 by a suitable process, such asspin-on coating, and patterned to form a patterned photoresist featureover the dummy gate electrode layer 308 by a proper lithographypatterning method. In at least one embodiment, a width of the patternedphotoresist feature over the P-active region 204 p and isolation region206 is in the range of about 500 to 1000 nm. In another embodiment, awidth of the patterned photoresist feature over the N-active region 204n is in the range of about 10 to 30 nm. The patterned photoresistfeature can then be transferred using a dry etching process to the dummygate electrode layer 308 to form a first dummy strip 308 a over theP-active region 204 p and isolation region 206 and a second dummy strip308 b over the N-active region 204 n. The photoresist layer may bestripped thereafter.

It is noted that the CMOS semiconductor device 200 may undergo other“gate last” processes and other CMOS technology processing to formvarious features of the CMOS semiconductor device 200. As such, thevarious features are only briefly discussed herein. The variouscomponents of the CMOS semiconductor device 200 may be formed prior toformation of the P-metal gate electrode 210 p and N-metal gate electrode210 n in a “gate last” process. The various components may comprisep-type and n-type lightly doped source/drain (LDD) regions (not shown)and p-type and n-type source/drain (S/D) regions (not shown) in theactive regions 204 p, 204 n and on opposite sides of the first dummystrip 308 a and second dummy strip 308 b. The p-type LDD and S/D regionsmay be doped with B or In, and the n-type LDD and S/D regions may bedoped with P or As.

Then, a dielectric layer is formed over the P-active region 204 p,N-active region 204 n, and isolation region 206 to produce the structureshown in FIG. 3B. The dielectric layer may comprise a single layer ormultilayer structure. In at least one embodiment, the dielectric layeris patterned to form gate spacers 304 on opposite sidewalls of the firstdummy strip 308 a and the second dummy strip 308 b. The gate spacers 304may be formed of silicon oxide, silicon nitride or other suitablematerials deposited by a CVD process.

Then, an inter-layer dielectric (ILD) material may be formed over thegate spacers 304, first dummy strip 308 a, second dummy strip 308 b, andisolation region 206. The ILD layer material may include an oxide formedby a high-aspect-ratio process (HARP) and/or a high-density-plasma (HDP)deposition process. After the ILD layer material deposition, a chemicalmechanical polishing (CMP) is performed on the ILD layer materialdeposition to expose the first dummy strip 308 a and second dummy strip308 b.

In the present embodiment, the remaining ILD layer material afterperforming the CMP process comprises a first portion 306_1 and a secondportion 306_2 surrounding the first dummy strip 308 a over the P-activeregion 204 p and isolation region 206. In addition, the remaining ILDlayer material comprises the second portion 306_2 and a third portion306_3 surrounding the second dummy strip 308 b over the N-active region204 n. Thus, the first dummy strip 308 a over the P-active region 204 pand isolation region 206 and the second dummy strip 308 b over theN-active region 204 n together define an ILD layer 306. Further, thefirst dummy strip 308 a comprises a first portion 308 a_1 and a secondportion 308 a_2.

The method 100 in FIG. 1 continues with step 106 in which the structurein FIG. 3C is produced by removing the first portion 308 a_1 of thefirst dummy strip 308 a to form a first opening 310 a extending overentire length of the P-active region 204 a in the ILD layer 306. In thepresent embodiment, using a patterned photoresist layer 312 as a mask,the first portion 308 a_1 of the first dummy strip 308 a is removed toform the first opening 310 a in the first dummy strip 308 a, while asecond portion 308 a_2 of the first dummy strip 308 a, the second dummystrip 308 b, and ILD layer 306 are covered by the patterned photoresistlayer 312. In the present embodiment, the first opening 310 a has thefirst width W₁ in the range of about 500 to 1000 nm.

In at least one embodiment, the first portion 308 a_1 of the first dummystrip 308 a may be removed using a dry etch process. In at least oneembodiment, the dry etch process may be performed under a source powerof about 650 to 800 W, a bias power of about 100 to 120 W, and apressure of about 60 to 200 mTorr, using Cl₂, HBr, and/or He as etchinggases. The patterned photoresist layer 312 may be stripped thereafter.

It should be noted that the dry etching process for removing the firstportion 308 a_1 of first dummy strip 308 a is especially prone tosimultaneously removing a top portion of the ILD layer 306_1/306_2adjacent to the first dummy strip 308 a. Thus, if recesses are generatedin the ILD layer 306_1/306_2 after dry etching the first portion 308 a_1of the first dummy strip 308 a, the recesses present in the ILD layer306_1/306_2 can become a receptacle of metals during subsequentprocessing thereby increasing the likelihood of electrical shortingand/or device failure.

In the present embodiment, the ILD layer 206 is covered and protected bythe patterned photoresist layer 312 while removing the first portion 308a_1 of the first dummy strip 308 a. The remaining second portion 308 a_2of the first dummy strip 308 a adjacent to the ILD layer 306_1/306_2 mayfurther protect the ILD layer 306_1/306_2 during a metal CMP process innext step 108. Accordingly, Applicant's method of fabricating a CMOSsemiconductor device 200 may fabricate the gate structure 210 havingalmost no recess in the ILD layer 306_1/306_2, thereby achieving aperfect isolation between neighboring transistors and thus enhancing thedevice performance.

The method 100 in FIG. 1 continues with step 108 in which the structurein FIG. 3D is produced by filling the first opening 310 a with thesecond metal composition 210 s. In at least one embodiment, the secondmetal composition 210 s may comprise a P-work-function metal. In someembodiments, the P-work-function metal comprises TiN, WN, TaN, or Ru.The P-work-function metal may be formed by ALD, CVD or other suitabletechnique. In the present embodiment, the second metal composition 210 sis first deposited to substantially fill the first opening 310 p. Then,a CMP process is performed to remove a portion of the second metalcomposition 210 s outside of the first opening 310 a. Accordingly, theCMP process may stop when reaching the ILD layer 306, and thus providinga substantially planar surface. The remaining second metal composition210 s is referred to as the bulk portion 210 b of the P-metal gateelectrode 210 p.

The method 100 in FIG. 1 continues with step 110 in which the structurein FIG. 3E is produced by removing a second portion 308 a_2 of the firstdummy strip 308 a to form a second opening 310 b (donated as 310 b_1 and310 b_2) over the isolation region 206 and by removing the second dummystrip 308 b to form a third opening 310 c extending over the entirelength of the N-active region 204 n in the ILD layer 306.

In the present embodiment, using the gate spacers 304, ILD layer 306 andbulk portion 210 b of the P-metal gate electrode 210 p as hard masks,the second portion 308 a_2 of the first dummy strip 308 a and the seconddummy strip 308 b are simultaneously removed to form the second andthird openings 310 b, 310 c in the ILD layer 306. In at least oneembodiment, the second opening 310 b has almost the same first width W₁of the first opening 310 a. In another embodiment, the third opening 310c has a second width W₂ in the range of about 10 to 30 nm, less than thefirst width W₁ of the first opening 310 a. A ratio of the first width W₁to the second width W₂ is from about 18 to 30.

In some embodiments, the second dummy strip 308 b and second portion 308a_2 of the first dummy strip 308 a may be removed using a wet etchand/or a dry etch process. In at least one embodiment, the wet etchprocess includes exposure to a hydroxide solution containing ammoniumhydroxide, diluted HF, deionized water, and/or other suitable etchantsolutions. In another embodiment, the dry etch process may be performedunder a source power of about 650 to 800 W, a bias power of about 100 to120 W, and a pressure of about 60 to 200 mTorr, using Cl₂, HBr and He asetching gases.

The method 100 in FIG. 1 continues with step 112 in which the structurein FIG. 3F is produced by filling the second and third openings 310 b,310 c with the first metal composition 210 f. In one embodiment, thefirst metal composition 210 f may comprise an N-work-function metal. Insome embodiments, the N-work-function metal comprises Ti, Ag, Al, TiAl,TiAlN, TaC, TaCN, TaSiN, Mn, or Zr. The N-work-function metal may beformed by ALD, PVD, sputtering or other suitable technique. In thepresent embodiment, the first metal composition 210 f is first depositedto substantially fill the second and third openings 310 b, 310 c. Then,a CMP process is performed to remove a portion of the first metalcomposition 210 f outside of the second and third openings 310 b, 310 c.Accordingly, the CMP process may stop when reaching the ILD layer 306,and thus providing a substantially planar surface.

In some embodiments, the remaining first metal composition 210 f in thesecond opening 310 b over the isolation region 206 is referred to as theendcap portion 210 e of the P-metal gate electrode 210 p. In the presentembodiment, the endcap portion 210 e of the P-metal gate electrode 210 phas a contact section connected to the bulk portion 210 b of the P-metalgate electrode 210 p. In the present embodiment, the endcap portion 210e of the P-metal gate electrode 210 p and the bulk portion 210 b of theP-metal gate electrode 210 p are combined and referred to as the P-metalgate electrode 210 p. In some embodiments, the remaining first metalcomposition 210 f in the third opening 310 c is referred to as theN-metal gate electrode 210 n. The P-metal gate electrode 210 p andN-metal gate electrode 210 n are combined and referred to as a metalgate structure 210.

FIG. 4 is a top view of an alternate CMOS semiconductor device 400comprising a metal gate structure 410 according to various aspects ofthe present disclosure fabricated using a method comprising the stepsshown in FIG. 3A-F, except that the first opening 310 a further extendsinto the isolation region 306 to form an extending portion. Similarfeatures in FIGS. 2 and 4 are numbered the same for the sake ofsimplicity and clarity. In the present embodiment, the endcap portion410 e comprises a second portion 410 e_2 and a first portion 410 e_1between the second portion 410 e_2 and the bulk portion 210 b, whereinthe second portion 410 e_2 comprises the first metal composition 210 f.A first length L₁ of the first portion 410 e_1 is equal to or less thana second length L₂ of the second portion 410 e_2. A ratio of the secondlength L₂ to the first length L₁ is from about 1.0 to 1.5.

In the present embodiment, the endcap portion 410 e of the P-metal gateelectrode 410 p and the bulk portion 210 b of the P-metal gate electrode410 p are combined and referred to as the P-metal gate electrode 410 p.The P-metal gate electrode 410 p and N-metal gate electrode 210 n arecombined and referred to as a metal gate structure 410.

It is understood that the CMOS semiconductor devices 200, 400 mayundergo further CMOS processes to form various features such ascontacts/vias, interconnect metal layers, dielectric layers, passivationlayers, etc.

Aspects of the present disclosure relate to a semiconductor device whichincludes a substrate including an isolation region surrounding aP-active region and an N-active region; a first gate electrode includinga first metal composition over the N-active region; and a second gateelectrode with a center portion over the P-active region and an endcapportion over the isolation region, wherein the endcap portion has thefirst metal composition, the center portion has a second metalcomposition different from the first metal composition, the centerportion and the endcap portion do not overlap, and an inner sidewall ofthe endcap portion is substantially aligned with a sidewall of theisolation region. In some embodiments, the endcap portion includes afirst portion over the isolation region at a first side of the centerportion, and a second portion over the isolation region over theisolation region at a second side of the center portion opposite fromthe first side of the center portion, and the first portion of theendcap portion is between the center portion and the second portion ofthe endcap portion. In some embodiments, a first width of the secondgate electrode is greater than a second width of the first gateelectrode. In some embodiments, a ratio of the first width to the secondwidth ranges from about 18 to about 30. In some embodiments, the firstmetal composition includes an N-work-function metal. In someembodiments, the first metal composition includes at least one of Ti,Ag, Al, TiAl, TiAlN, TaC, TaCN, TaSiN, Mn, or Zr. In some embodiments,the P-active region includes a source region and a drain region onopposite sides of the center portion. In some embodiments, thesemiconductor device includes a first type of lightly doped source/drain(LDD) regions in the N-active region, wherein the first type of LDDregions and the N-active region have the same type of dopants; and asecond type LDD regions in the P-active region, wherein the second typeof LDD regions and the P-active region have the same type of dopants,different from the first type of dopants. In some embodiments, thesecond metal composition includes a P-work-function metal. In someembodiments, the second metal composition includes at least one of TiN,WN, TaN, or Ru.

Aspects of the present disclosure relate to a semiconductor device whichincludes a substrate; a first well region in the substrate, the firstwell region having a first conductivity type; a second well region inthe substrate, the second well region having a second conductivity type;

a dielectric material in the substrate between the first well region andthe second well region; a first gate electrode which includes a firstmetal composition over the second well region; and a second gateelectrode which includes a center portion over the first well region andan endcap portion over the dielectric material, wherein the endcapportion includes the first metal composition, the center portionincludes a second metal composition different from the first metalcomposition, a bottom of the center portion and a bottom of the endcapportion are substantially coplanar, and an inner sidewall of the endcapportion is substantially aligned with a sidewall of the dielectricmaterial. In some embodiments, the center portion extends over an entirelength of the first well region. In some embodiments, the endcap portionincludes a first portion over the isolation region at a first side ofthe center portion, and a second portion at a second side over theisolation region at a second side of the center portion opposite formthe first side of the center portion, and the first portion of theendcap portion is positioned between the center portion and the secondportion of the endcap portion. In some embodiments, the first gateelectrode extends over an entire length of the second well region. Insome embodiments, a first width of the second gate electrode is greaterthan a second width of the first gate electrode. In some embodiments, asidewall of the center portion is substantially aligned with a sidewallof the first well region.

Aspects of the present disclosure relate to a semiconductor device whichincludes a substrate; a first active region in the substrate, the firstactive region having a first conductivity type; a second active regionin the substrate, the second active region having a second conductivitytype; a dielectric material in the substrate surrounding the firstactive region and the second active region; a first gate electrode whichincludes a first conductive material over the second active region,wherein the first gate electrode has a width extending beyond aperiphery of the second active region; and a second gate electrode whichincludes a center portion substantially aligned with the first activeregion in a direction of a channel and an endcap portion over thedielectric material abutting the center portion, wherein the endcapportion includes the first conductive material, the center portionincludes a second conductive material different from the firstconductive material, and an interface between the center portion and theendcap portion is substantially aligned with an interface between thesecond active region and the dielectric material. In some embodiments,the endcap portion includes a first portion over the dielectric materialat a first side of the center portion of the second gate electrode, anda second portion over the dielectric material at a second side of thecenter portion of the second gate electrode opposite from the first sideof the center portion. In some embodiments, a width of the centerportion is greater than a width of the first gate electrode. In someembodiments, the first gate electrode is separated from the endcapportion of the second gate electrode by a second dielectric materialover the dielectric material.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

What is claimed is:
 1. A semiconductor device comprising: a substratecomprising an isolation region surrounding a P-active region and anN-active region; a first gate electrode comprising a first metalcomposition over the N-active region; and a second gate electrodecomprising a center portion over the P-active region and an endcapportion over the isolation region, wherein the endcap portion comprisesthe first metal composition, the center portion comprises a second metalcomposition different from the first metal composition, the centerportion and the endcap portion do not overlap, and an inner sidewall ofthe endcap portion is substantially aligned with a sidewall of theisolation region.
 2. The semiconductor device of claim 1, wherein theendcap portion comprises a first portion over the isolation region at afirst side of the center portion, and a second portion over theisolation region over the isolation region at a second side of thecenter portion opposite from the first side of the center portion, andthe first portion of the endcap portion is between the center portionand the second portion of the endcap portion.
 3. The semiconductordevice of claim 1, wherein a first width of the second gate electrode isgreater than a second width of the first gate electrode.
 4. Thesemiconductor device of claim 3, wherein a ratio of the first width tothe second width ranges from about 18 to about
 30. 5. The semiconductordevice of claim 1, wherein the first metal composition comprises anN-work-function metal.
 6. The semiconductor device of claim 1, whereinthe first metal composition comprises at least one of Ti, Ag, Al, TiAl,TiAlN, TaC, TaCN, TaSiN, Mn, or Zr.
 7. The semiconductor device of claim1, wherein the P-active region comprise a source region and a drainregion on opposite sides of the center portion.
 8. The semiconductordevice of claim 1, further comprising: a first type of lightly dopedsource/drain (LDD) regions in the N-active region, wherein the firsttype of LDD regions and the N-active region have the same type ofdopants; and a second type LDD regions in the P-active region, whereinthe second type LDD regions and the P-active region have the same typeof dopants, different from the first type of dopants.
 9. Thesemiconductor device of claim 1, wherein the second metal compositioncomprises a P-work-function metal.
 10. The semiconductor device of claim1, wherein the second metal composition comprises at least one of TiN,WN, TaN, or Ru.
 11. A semiconductor device, comprising: a substrate; afirst well region in the substrate, the first well region having a firstconductivity type; a second well region in the substrate, the secondwell region having a second conductivity type; a dielectric material inthe substrate between the first well region and the second well region;a first gate electrode comprising a first metal composition over thesecond well region; and a second gate electrode comprising a centerportion over the first well region and an endcap portion over thedielectric material, wherein the endcap portion comprises the firstmetal composition, the center portion comprises a second metalcomposition different from the first metal composition, a bottom of thecenter portion and a bottom of the endcap portion are substantiallycoplanar, and an inner sidewall of the endcap portion is substantiallyaligned with a sidewall of the dielectric material.
 12. Thesemiconductor device of claim 11, wherein the center portion extendsover an entire length of the first well region.
 13. The semiconductordevice of claim 12, wherein the endcap portion comprises a first portionover the dielectric material at a first side of the center portion, anda second portion at a second side over the dielectric material at asecond side of the center portion opposite form the first side of thecenter portion, and the first portion of the endcap portion ispositioned between the center portion and the second portion of theendcap portion.
 14. The semiconductor device of claim 11, wherein thefirst gate electrode extends over an entire length of the second wellregion.
 15. The semiconductor device of claim 11, wherein a first widthof the second gate electrode is greater than a second width of the firstgate electrode.
 16. The semiconductor device of claim 11, wherein asidewall of the center portion is substantially aligned with a sidewallof the first well region.
 17. A semiconductor device, comprising: asubstrate; a first active region in the substrate, the first activeregion having a first conductivity type; a second active region in thesubstrate, the second active region having a second conductivity type; adielectric material in the substrate surrounding the first active regionand the second active region; a first gate electrode comprising a firstconductive material over the second active region, wherein the firstgate electrode has a width extending beyond a periphery of the secondactive region; and a second gate electrode comprising a center portionsubstantially aligned with the first active region in a direction of achannel and an endcap portion over the dielectric material abutting thecenter portion, wherein the endcap portion comprises the firstconductive material, the center portion comprises a second conductivematerial different from the first conductive material, and an interfacebetween the center portion and the endcap portion is substantiallyaligned with an interface between the second active region and thedielectric material.
 18. The semiconductor device of claim 17, whereinthe endcap portion comprises a first portion over the dielectricmaterial at a first side of the center portion of the second gateelectrode, and a second portion over the dielectric material at a secondside of the center portion of the second gate electrode opposite fromthe first side of the center portion.
 19. The semiconductor device ofclaim 17, wherein a width of the center portion is greater than a widthof the first gate electrode.
 20. The semiconductor device of claim 19,wherein the first gate electrode is separated from the endcap portion ofthe second gate electrode by a second dielectric material over thedielectric material.